Good day to you.
First off. welcome. second, as its your FIRST post I hope you wont get flamed too hard because there are many many threads that cover the pros/cons of rooting.
I suggest next time you have a question, take a minute to use the search function (and post in the right forum! questions go in Q&A).
A few quick pros of rooting.
Free wireless tether (sharing your phones internet connection with a laptop or other wifi enabled device)
The ability to flash custom ROMs, these are the operating systems of the phone, they're all built off of (for the most part) stock htc/sprint images, but there are plenty and many options, find one that suits your needs and try it out.
Custom kernels, they are the set of drivers and the "brain" of your phone, want it overclocked? get a custom kernel, want it undervolted (Save battery) get a custom kernel. many options to choose from
Custom Boot screens.
Root only applications, titanium backup (backs up stuff, i dont use it so i cant elaborate), shootme (screenshot program) and others im sure.
Hope this clears up some stuff, welcome, use the search (really im just trying to help ya here) and have fun!